1. Field of the Invention
The present invention relates to a wiring board with a columnar conductor protruding from a first main surface of the wiring board. More specifically, the present invention relates to a wiring board with a columnar conductor that is capable of improving reliability when mounted on a mounting substrate, such as a motherboard, and also relates to a method of making the same.
2. Description of the Related Art
One example of this type of wiring board is a multilayer ceramic board described in Japanese Unexamined Patent Application Publication No. 09-083141. The multilayer ceramic board is used as a chip-size packaging wiring board. To make a chip-size package, a semiconductor device is disposed on a projection electrode protruding from a multilayer ceramic board, the gap between the multilayer ceramic board and the semiconductor device is sealed with resin, and the semiconductor device is fixed to the multilayer ceramic board. That is, the semiconductor device is connected to a composite multilayer board including the multilayer ceramic board and the resin layer, and the protruding end surface of the projection electrode of the multilayer ceramic board and the surface of the resin layer are arranged so as to be substantially flush with each other.
The multilayer ceramic board having the projection electrode is obtained by disposing, on the upper surface of laminated green ceramic sheets for use in a board, a shrinkage suppressing sheet that includes an opening at a location corresponding to a via conductor passing through the laminated ceramic sheets defining a board and having a size to fit a projection electrode and that has a thickness corresponding to the height of the projection electrode, firing the composite, and utilizing firing shrinkage in the direction of the thickness of the ceramic sheets.
Here, the projection electrode described in Japanese Unexamined Patent Application Publication No. 09-083141 is an electrode used to dispose a semiconductor device on a multilayer ceramic board. When this projection electrode is used for a structure arranged to dispose the multilayer ceramic board on a motherboard, such as printed wiring board, one example of such a structure is illustrated in FIG. 19. That is, the example shown in FIG. 19 includes a semiconductor device 54 that is disposed on one main surface of a multilayer ceramic board 51, projection electrodes 52 arranged to connect the multilayer ceramic board 51 and a motherboard (not shown) are provided in the vicinity of the semiconductor device 54, and a resin layer 53 is provided such that the tip surface of each of the projection electrodes 52 is exposed.
However, with this structure, because the projection electrode 52 is embedded in the resin layer 53 and the upper end surface of the projection electrode 52 is substantially flush with the upper surface of the resin layer 53, in order to mount the multilayer ceramic board 51 on the motherboard, the projection electrode 52 of the multilayer ceramic board 51 and a surface electrode of the motherboard are connected to each other. However, in this case, because the motherboard and the resin layer 53 are substantially in close contact with each other, if the motherboard is distorted by, for example, thermal expansion and is curved toward the resin layer 53, the motherboard pushes the resin layer 53 upward. As a result, the multilayer ceramic board 51 may be disconnected from the motherboard or a crack may be produced in the multilayer ceramic board 51. If the semiconductor device 54 is disposed on the multilayer ceramic board 51, the semiconductor device 54 may be separated from the multilayer ceramic board 51.
When the semiconductor device 54 is mounted on the multilayer ceramic board 51 and the semiconductor device 54 and the multilayer ceramic board 51 are substantially entirely sealed with resin, the amount of resin required is relatively large. In this case, the curing shrinkage of the resin layer 53 may be increased, and the multilayer ceramic board 51 may be warped. As a result, the mounting on the motherboard may be difficult.